The present invention relates to synchronous motors for clocks capable of being operated through a single energizing winding.
Such synchronous motors are generally so designed that magnetic flux induced in the stator by an AC energized winding or windings is distributed around the rotor consisting of a thin cylindrical permanent magnet and a pair of discs made of permeable materials, each of which discs has a plurality of north or south poles on its periphery and between which discs the permanent magnet is sandwiched in, so as thereby to cause rotor to rotate.
The application of such synchronous motors to electric clocks, or the like, has been regarded as being advantageous in view of the fact that the necessity for converting the reciprocating motion, of a balance wheel, pendulum, or the like, into rotary motion may be eliminated thereby.
Two types of synchronous motors have hitherto been developed, one type being so constructed that AC induced magnetic fluxes are generated through plural winding coils arranged around the rotor, while the other type being so constructed that AC induced magnetic flux is generated around the rotor through a single winding coil. The motor of the former type has been unable to be applied in electric clocks in view of its expensiveness as well as its incapability of rotating at low speeds, while the motor of the latter type has hitherto been applied to the electric clocks because of its simple structure, inexpensiveness and capability of rotating at low speeds. However, the synchronous motor of the latter type (such motor will be merely called "the motor" hereinafter in the specification and claims) operates at a low efficiency in general, so that, even if the stator magnetic circuit and the rotor discs are made of highly permeable materials, the motor has not been able to be applied to battery powered clocks without changing or recharging the batteries within a shorter period. As for the above-mentioned highly permeable materials, for example, "METALS HANDBOOK", 8th Edition, Vol. 1, pp. 794-797, 1961 (published by American Society for Metals) is referred to.